<template>
  <transition>
    <div ref="dragIcon"
         class="dragIcon"
         @touchstart.stop="handleTouchStart"
         @touchmove.prevent.stop="handleTouchMove($event)"
         @touchend.stop="handleTouchEnd"
         :style="{left: left + 'px',top: top + 'px',width: itemWidth + 'px',height: itemHeight + 'px'}"
         v-if="isShow">
      <template v-if="!$slots.content">{{text}}</template>
      <slot name="content" />
    </div>
  </transition>
</template>

<script>
export default {
  props: {
    text: {
      type: String,
      default: '球'
    },
    itemWidth: {
      type: Number,
      default: 40
    },
    itemHeight: {
      type: Number,
      default: 40
    }
  },
  data () {
    return {
      left: 0,
      top: 0,
      startToMove: false,
      isShow: true,
      timer: null,
      currentTop: null,
      clientW: document.documentElement.clientWidth,//视口宽
      clientH: document.documentElement.clientHeight,//视口高
    }
  },
  created () {
    this.left = (this.clientW - this.itemWidth - 30)
    this.top = (this.clientH / 2 - this.itemHeight / 2)
  },
  mounted () {
    this.bindScrollEvent()
  },
  beforeDestroy () {
    // 记得销毁一些全局的的事件
    this.removeScrollEvent()
  },
  methods: {
    handleTouchStart () {
      this.startToMove = true
      this.$refs.dragIcon.style.transition = "none"
    },
    handleTouchMove (e) {
      const clientX = e.targetTouches[0].clientX;//手指相对视口的x
      const clientY = e.targetTouches[0].clientY;//手指相对视口的y
      const isInScreen = clientX <= this.clientW && clientX >= 0 && clientY <= this.clientH && clientY >= 0
      if (this.startToMove && e.targetTouches.length === 1) {
        if (isInScreen) {
          this.left = clientX - this.itemWidth / 2
          this.top = clientY - this.itemHeight / 2
        }
      }
    },
    handleTouchEnd () {
      if (this.left < (this.clientW / 2)) {
        this.left = 30;//不让贴边 所以设置30没设置0
        this.handleIconY()
      } else {
        this.left = this.clientW - this.itemWidth - 30;//不让贴边 所以减30
        this.handleIconY()
      }
      this.$refs.dragIcon.style.transition = "all .3s"
    },
    handleIconY () {
      if (this.top < 0) {
        this.top = 30;//不上帖上边所以设置为30 没设置0
      } else if (this.top + this.itemHeight > this.clientH) {
        this.top = this.clientH - this.itemHeight - 30;//不让帖下边所以减30
      }
    },
    bindScrollEvent () {
      window.addEventListener('scroll', this.handleScrollStart)
    },
    removeScrollEvent () {
      window.removeEventListener('scroll', this.handleScrollStart)
    },
    handleScrollStart () {
      this.isShow = false
      this.timer && clearTimeout(this.timer)
      this.timer = setTimeout(() => {
        this.handleScrollEnd()
      }, 300)
      this.currentTop = document.documentElement.scrollTop || document.body.scrollTop
    },
    handleScrollEnd () {
      this.scrollTop = document.documentElement.scrollTop || document.body.scrollTop
      // 判断是否停止滚动的条件
      if (this.scrollTop == this.currentTop) {
        this.isShow = true
      }
    }
  },
}
</script>

<style scoped>
.dragIcon {
  position: fixed;
  z-index: 9999;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  /* background-color: #007aff; */
  background-image: linear-gradient(172deg, #405996 13%, #4073f5 91%);
  line-height: 40px;
  text-align: center;
  color: #fff;
}
.v-enter {
  opacity: 1;
}
.v-leave-to {
  opacity: 0;
}
.v-enter-active,
.v-leave-active {
  transition: opacity 0.3s;
}
</style>